A brand new computer needs to be personalized with whatever hardware and software you are going to need, whether for business, entertainment or both. Most computers come with a CPU unit, keyboard, screen, mouse and speakers, which is a very basic configuration.
Compare customizing your computer to baking a loaf of bread. You might just use a plain bread recipe and the results will be a plain loaf of bread. Alternatively, you could add fruit and nuts for a more interesting bread, or cheese and mustard for something very different! My point is that it is totally up to you.
Accessorizing does not have to be expensive. You might decide, for example, that you want a printer and scanner in one and a webcam. You might want a digital camera so you can upload photos on to your computer and email them to your friends. You might want surround sound speakers if you plan to download and watch movies on your computer.
If you want to create digital artwork, you need a good graphics tool. If you want to talk to family or friends on the other side of the world, you can do so by sending emails. Or you might want a microphone and headset and a webcam. This ultimately works out cheaper than phone calls and definitely cheaper than plane tickets.
It is not necessary to buy all the extras at once but if you have a good idea of what you want to use your computer for, it is easier to buy everything at once and install it all. Then you have it when you need it. Extras such as webcams, printers and scanners do not normally come included with the computer. Different people prefer different makes and models, depending on their budget and what they plan to use the hardware for.